NEW YORK — Dr. John F. Rosen, a pediatrician whose discovery of high levels of lead poisoning among the New York City children he treated propelled him to campaign for a national effort to prevent the condition, died Dec. 7 in Greenwich, Conn. He was 77.

When he arrived at Montefiore Medical Center in the Bronx in 1969, Dr. Rosen was mainly interested in how children’s bodies absorb calcium. But within a few years, concerned about the levels of lead he was seeing in his young patients and knowing that lead poisoning diminished mental capacities irre­versibly, he embarked on a mission. Dr. Rosen helped establish one of the nation’s first and largest clinics for the treatment of lead poisoning; he personally supervised the treatment of 30,000 children. In one advance, he developed X-ray techniques for measuring lead in children’s bodies.

He went on to push New York City to adopt stricter standards for removing lead paint from tens of thousands of old buildings. (The use of lead paint had been outlawed in 1978.) In 1991 he led a committee at the Centers for Disease Control and Prevention in Atlanta that lowered the threshold at which children are considered to be poisoned by lead, to 10 micrograms per deciliter of blood from 60 micrograms.

But that threshold was too high, Dr. Rosen believed, and he immediately lobbied to ­reduce it further. This year, the CDC halved it to 5 micrograms. The change could not help those who had lead in their bodies, but it sounded an alarm that even infinitesimal quantities of lead could be dangerous.

‘’It’s about time,’’ he said.

He cited his own and others’ studies showing that lead poisoning harms a person’s ability to think and plan, as well as physical coordination. For a child with an IQ of 85, he said, lead exposure ‘‘could mean the difference between a menial job in a fast-food restaurant or a meaningful career.’’

Dr. Rosen’s ambition was to eventually eradicate lead poisoning by eliminating exposure to lead ­altogether, in the manner that vaccines reduced the incidence of polio to almost none. He served on committees of the National Academy of Sciences and urged spending tens of billions of dollars to ­remove old lead paint from tens of millions of homes, calculating that lead exposure harmed far more children than asbestos.